Solar wind velocity reconstruction at Mercury using MESSENGER bow shock and magnetopause crossings.

The solar wind significantly shapes and influences planetary magnetospheres, driving their structure and dynamics. Mercury, with its weak intrinsic magnetic field and close proximity to the Sun, is particularly sensitive to solar wind variations and adapts quickly to solar wind changes. Understanding solar wind characteristics, such as flow speed, is essential for fine-tuning magnetospheric models and eventually for interpreting Mercury’s magnetospheric response to solar wind changes. The solar wind speed affects both the aberration angle, which tilts the magnetosphere relative to the Mercury-Sun line, and the subsolar standoff distances from the internal dipole center of both the bow shock as well as the magnetopause.

This study reconstructs solar wind speeds from various bow shock and magnetopause crossings observed in-situ by MESSENGER’s magnetometer. We fit empirical bow shock and magnetopause models to the aberration angle and treat the subsolar standoff distances as additional parameters. For single crossings, a strong correlation between the parameters emerges. Thus, they cannot be independently determined, resulting in an infinite set of possible solutions for solar wind speed. To alleviate this problem, we combine multiple crossings to find a common aberration angle. Here, we present and discuss the first statistical results from the analysis and compare them to average boundary shapes and positions.